1. Field of the Invention
The present invention relates to an optical module and a method for manufacturing the same, and more particularly, to an optical module, in which one or more grooves, in which are mounted a plurality of optical fibers or optical parts are formed to different depths and a stopper hole is manufactured so as to prevent a convex corner phenomenon so that an optical axis is precisely aligned, and a method for manufacturing the same.
2. Description of the Related Art
Recently, transmission methods in an optical communication system have been replaced by wavelength division multiplexing (WDM) transmission methods, with increase in transmission data in an optical communication network. As connection between networks is required in the WDM system, an optical crossing connector (OXC), that is, an optical module, is an essential element.
Referring to FIG. 1A, the optical module includes a micro-mirror 10, an actuator 15 for driving the micro-mirror 10, an input optical fiber 20 for transmitting an optical signal to the micro-mirror 10 around the actuator 15, an output optical fiber 22 for receiving an optical signal reflected from the micro-mirror 10 and transmitting the optical signal, and an optical module 30 in which ball lenses 25 and 27, aligned for focusing light, are arranged between the input and output optical fibers 20 and 22 and the micro-mirror 10. The input and output optical fibers 20 and 22 are arranged in the V-grooves 35, and the ball lenses 25 and 27 are arranged in micro-pits 40 which communicate with the V-groove 35. The optical fibers 20 and 22, the ball lens 25, and the micro-mirror 10 are all aligned with an optical axis.
In the optical module having the above structure, an optical signal transmitted from the input optical fiber 20 passes through the ball lens 25, is reflected by the micro-mirror 10, passes through the ball lens 27, and is output through the output optical fiber 22 and transmitted to a predetermined place. The ball lenses 25 and 27 focus the optical signal to reduce optical loss and to minimize the optical path.
As shown in FIG. 1B, a convex corner 45 is formed in a portion where a hole 17 for installing the actuator 15 is connected to the micro-pit 40 and the micro-pit 40 is connected to the V-grooves 35. Since the sizes of the actuator 15, the ball lenses 25 and 27, and the optical fibers 20 and 22 are different, the depths of the hole 17, the V-groove 35, and the micro-pit 40 for receiving these elements must be different in order to align their centers on the optical axis.
However, when manufacturing the optical module having the above structure by etching, the optimum conditions for etching such as time or temperature, are different according to the width or depth of the groove to be etched. In other words, since the hole 17, the V-groove 35, and the micro-pit 40 have different widths and depths, etching must be performed under different conditions for the hole 17, the V-groove 35, and the micro-pit 40. However, in the prior art, etching is performed by patterning once, under the ideal conditions for only one of the hole 17, the V-groove 35, and the micro-pit 40, or under conditions which are the average of the ideal conditions for the hole 17, the V-groove 35, and the micro-pit 40. Thus, in this case, the conditions for etching are not appropriate for the other regions except for the groove when the groove is a standard, and etching cannot be performed as patterned; defects in etching occur even under the average conditions.
In particular, a convex corner phenomenon in which the shapes of the micro-pit 40 or the hole 17 are not precisely etched and their pattern shapes are damaged, occurs in the convex corner 45 of the micro-pit 40 or the hole 17. FIG. 1B illustrates that the patterns of the convex corners 45 before etching are greatly damaged after etching. Due to damage of the convex corner 45, the standard of correct dimensions as designed cannot be obtained, and thus, the arrangement of optical elements such as the optical fibers 20 and 22, or the ball lenses 25 and 27, varies. As a result, the optical axes of the elements are not aligned, and thus, the optical signal cannot be precisely transmitted, thereby causing optical loss.
Thus, in order to prevent damage to patterns caused by the convex corner effect, specific corner compensation patterns 50 and 52 as shown in FIG. 2 are required. That is, in consideration of the convex corner effect, compensation patterns for supplementing are formed on an etching mask 65 so that the phenomenon during etching is suppressed, allowing the optical module to be manufactured with the desired shape. Here, reference numerals 17′ and 40′ denote a hole area and a micro-pit area, which are formed in the etching mask 65, respectively.
A method for manufacturing an optical module using the corner compensation patterns 50 and 52 will be described as follows.
As shown in FIGS. 3A and 3B, silicon dioxide (SiO2) 63 is coated on a upper silicon wafer 60 of (100) in which both surfaces of the upper silicon wafer 60 are polished, and silicon nitride (Si3N4) 65 is deposited on both surfaces of the upper silicon wafer 60 using a low pressure chemical vapor deposition (LPCVD) method so that silicon dioxide 63 can be used as a silicon etching mask on the upper silicon wafer 60. Next, as shown in FIG. 3C, silicon nitride (Si3N4) layers 65 on both surfaces of the upper silicon wafer 60 are patterned by a reactive ion etching (RIE) process. The corner compensation patterns 50 and 52 are added to the silicon nitride (Si3N4) layers 65 so that the pattern shapes are not damaged by the convex corner effect during etching.
Also, as shown in FIGS. 4A and 4B, silicon oxide (SiO) 72 and silicon nitride (Si3N4) 75 are sequentially deposited on a lower silicon wafer 70 and are patterned by the RIE process, as shown in FIG. 4C.
Next, anisotropic wet etching of the upper and lower silicon wafers 60 and 70 is performed using a KOH aqueous solution, thereby forming a V-groove area 67, a micro-pit area 68, and hole areas 69 and 69′, as shown in FIGS. 3D and 4D. The upper and lower silicon wafers 60 and 70 are bonded together, as shown in FIGS. 5A and 5B.
The actuator 15 for a micro-mirror is installed in the hole 17 of the optical module, and the optical fibers 20 and 22, and the ball lenses 25 and 27 are installed respectively in the V-groove 35 and the micro-pit 40, to be aligned with the optical axis.
At present, the optical module is manufactured by the above-mentioned manufacturing process, using the corner compensation patterns 50 and 52. However, the corner compensation patterns 50 and 52 are appropriate only when there is a minor difference in depth between the V-groove 35 and the micro-pit 40, and their length should be three times the etching depth. The corner compensation patterns 50 and 52 complicate and enlarge the entire patterns for manufacturing the optical module.
Also, if the location of the optical axis is changed, the depth of etching must also be changed, requiring new compensation patterns. In other words, the compensation patterns 50 and 52 must be designed according to the width or depth of the micro-pit 40 or the hole 17. Thus, whenever the optical axis varies, new compensation patterns must be prepared.
In particular, since the compensation patterns 50 and 52 become complicated where input/output terminals of the optical fibers are adjacent, or where the convex corner effect occurs greatly, the optical path cannot be minimized, causing optical loss due to differences in the optical path. Furthermore, as the number of channels of the optical module increases, it is difficult to form the compensation patterns, and part of the convex corner 45′ can be damaged, even though the compensation patterns are used, as shown in the photo of FIG. 6, and thus the requirements for miniature optical elements cannot be satisfied.